Temporal and spatial variations of the epilithic phycoflora were studied in one of the largest streams at Hope Bay (Antarctic Peninsula) during the summer of 1992/93. A complete floristic inventory was made, and the relative frequencies of each algal taxon were estimated. Periphytic cumulative chlorophyll a was measured by means of artificial substrata. The stream was a typical maritime Antarctic lotic ecosystem, with evident signs of enrichment by sea-birds. Variability in discharge strongly affected the water chemistry, with the high water level periods characterized by the lowest conductivities and dissolved reactive phosphorus concentrations. Epilithic algal communities predominantly consisted of algal mats or filamentous and foliose forms of Prasiola crispa. Other dominant species were Leptolyngbya fragilis, Hydrurus foetidus, Chrysococcus cf. rufescens and Phaeogloea mucosa. Whereas P. crispa appeared more frequently near to the origin of the stream in Boeckella Lake, Chrysophyceae were better developed towards the mouth.
